This invention relates to an exhaust gas recycling device for an internal combustion engine and more particularly to an improved control for exhaust gas recirculation.
In connection with controlling the emission of unwanted exhaust gas constituents from internal combustion engines, it is a widely adapted technique to recirculate a portion of the exhaust gases back to the combustion chambers. Such exhaust gas recirculation (EGR) has the effect of reducing the temperature in the combustion chamber and, accordingly, the emission of nitrous oxides. It has been the practice to reintroduce the exhaust gases into the induction system for mixing with the intake charge prior to induction into the combustion chambers. However, the induction system vacuum varies considerably with engine load and, therefore, the effective control of the amount of exhaust gas recirculation is seriously hampered. Furthermore, the introduction of the exhaust gases into the intake system has a tendency to create a higher than desired degree of exhaust gas recirculation at low loads and a lower than desirable degree of exhaust gas recirculation at high loads. Furthermore, due to the elevated temperature of the exhaust gases, the exhaust gas recirculation has a tendency to cause the engine to run hotter than desired and also tends to create unnecessarily high temperatures in the combustion chamber under certain conditions.
It is, therefore, a principal object of this invention to provide an improved device for controlling exhaust gas emissions through the use of exchaust gas recirculation.